text:
To what extent is modern "maneuverable spy balloonery" really a thing?
There's a high altitude balloon in the news recently. It seems to have come from the Pacific, passed over Canada and is now over the US. I don't have any official tracking data but notional trajectories are shown in screenshots below. The CNN graphic is labeled conservatively:

Potential trajectory: suspected spy balloon

Question: Balloons certainly have a place in the history of warfare and intelligence gathering, but these days are there really noted, plausible modern instances of spy balloonery? And are investigative balloons (spy or otherwise) of this size really maneuverable?

screenshots from CNN's February 4, 2023 See path the suspected spy balloon may have taken showing a "potential trajectory" of a "suspected spy balloon" and some high resolution photos showing the balloon and an array of panels that seem likely to be for solar power.

A different hypothetical map from Sky News's February 4, 2023 Spy balloon: China wanted 'to be noticed' says Professor Michael Clarke showing a trajectory for an object at 40,000 feet ending up in Montana

Screenshot from the April 30, 2020 NASA Wallops video B-Line to Space: The Scientific Balloon Story showing the payload and its solar panels. I don't know which balloon mission this is, but we can see images of another similar one in Space SE's What cosmic ray sensor is attached to this Balloon?
From the video:

NASA’s Wallops Flight Facility in Virginia manages the agency’s Scientific Balloon Program with 10 to 15 flights each year from launch sites worldwide. Northrop Grumman, which operates NASA’s Columbia Scientific Balloon Facility (CSBF) in Texas, provides mission planning, engineering services and field operations for the program. The CSBF team has launched more than 1,700 scientific balloons in the over 35 years of operation.

different but related: What other times has a Chinese high-altitude balloon entered US airspace?

To what extent is modern "maneuverable spy balloonery" really a thing?

To the extent that it helps to sell news and stoke irrational fear of secret Chinese technology.
Much of what a "spy balloon" can accomplish can be done better with a satellite. But there is maybe one thing for which a balloon is the better option: Signal intelligence, meaning the listening in on radio signals. This could be anything from intercepting radio communications to provoking air defenses in order to learn what frequencies and tactics are used.
The "navigating" part is rather limited. Other than changing altitude in order to catch a different wind direction there is nothing a balloon can do for flying into a certain direction. Altitude changes happen automatically with the heating of the balloon from solar radiation and cooling again during the night. In order to deliberately change altitude, ballast must be carried along in order to be dropped when the balloon should climb.
To me it looks as if the balloon flew into US airspace by chance and not by active control.

EDIT (Feb. 18, 2023): Aviation Week cites an ex-Google Loon engineer with the information that in the most recent balloons altitude is controlled by a ballonet, an internal gas bag that can be in- or deflated to change the pressure (and thus the buoyancy) of the balloon:

The most advanced ultra-long-endurance, high-altitude balloons seldom use propellers for directional control. Instead, such aircraft pump regular air into an internal ballonet envelope to descend or release the air to climb, Bowen says. Altitude adjustments are made to find wind currents moving in other directions. The system provides a limited capability for directional control.

Thanks. "by chance" because despite potentially being able to control altitude, the winds at 40,000 to 60,000 feet are unpredictable?

Are there no other feasible mechanisms of navigation? Could small jets within the balloon expel material to change course. Could some liquid ballast be released to raise altitude. Could some helium gas be expelled to decrease altitude?
Can someone calculate what altitude the current Chinese balloon SHOULD have, based on its approximate size and if it were filled to capacity with helium? Can we then tell from that value what the range of vertical maneuverability should be?

@uhoh This is the altitude for jet stream winds, so a small change in altitude could potentially make a big difference in speed. Direction is harder to control and really a matter of chance.

@JohnPankowicz In principle yes, but given the massive drag of a large balloon, this would be rather inefficient and only allow only for small distances of powered travel.

"can be done better with a satellite"  which would cost a lot more.

@PeterKämpf Okay thanks .I'm slowly working through this. Assuming it has the ability to change its altitude and a microcontroller with GPS (and a suitable algorithm), then in that case the "by chance" would have to come from lack of availability of suitable wind directions. These suggest there's been opportunity to develop the navigation, and this security analyst suggests (without details or specifics) that at both 40,000 and 60,000 feet it ends up over Montana, using "NOAA data". So I guess that's what I'll need to learn about.

@PeterKämpf ..this is at forty thousand feet which is a bit low but if you look at the winds at 40,000 feet that's where the balloon would have come from from China across the Aleutian Islands across Alaska and into the United States we put another model onto it at about 60 000 feet which is more of the operational height it'll be at but that gives it a slightly different track but it still ends up over Montana. I'll do some poking around and see what I can learn about the jet stream winds and if I can formulate a followup question here or in Earth Science

In addition to signal intelligence, being 10x closer than the lowest-dipping spy satellites and moving 50x more slowly and being in the atmosphere also allows one to pick up other information as well. A sensitive single crystal germanium detector can pick up trace signatures of radioisotopes (if there's some unshielded activity or transportation) and one can "sniff" the air for particulates. Yes this sounds a bit like a Michael Crichton novel I know, but with spook stuff we (us non spooks) really never know for sure.

It seems that a team of researchers from Loon, an ex "Google X" project, used deep learning to predict wind currents in the stratosphere to move balloons around by changing altitude (See also here, "Sailing the stratosphere" paragraph). It sounds plausible that the Chinese military is able to do something similar.

@uhoh You can try various trajectories of particles yourself. These kind of models are used, e.g., for volcanic ash prediction https://www.ready.noaa.gov/HYSPLIT_traj.php

@uhoh And this is how such model outputs can be used to optimize balloon trajectories https://www.ready.noaa.gov/READY_balloon.php

@uhoh Technically, couldn't that be equally well achieved by renting a private plane and flying around?

Within days of each other, one such balloon shows up in Montana and another in Latin America. It's extremely difficult to imagine that both of these locations were predetermined and the balloons were guided to their targets by cutting edge technology.

@PeterKämpf Crichton could make it work somehow, but yeah, unless the balloon went somewhere planes are excluded, like over a sensitive military installation or something...

@VladimirFГероямслава thanks! It may now be harder to ask a follow up question to which those would be part of the answer, but I'll keep working on it.

@PeterKämpf Just an FYI, I have significant experience with balloons that altitude station-keep for one full sun cycle.  The balloon has a small amount of ballast and a controllable gas vent.  We vent gas as solar radiation heats the envelope to maintain a fixed GPS altitude.  At night, we dump ballast as the lack of solar radiation cools the envelope.  The certification on our balloons only allowed us to carry enough ballast weight for one cycle, but by planning launch times we could get 30-ish hours at an altitude.  That's about 900 linear miles of flight at FL 1200 in the US latitudes.

@uhoh I wouldn't assume that the balloon has any super-secret signals intelligence gathering or photo-reconnaissance mission.  Quite often the intelligence objective is geo-political.  Flying balloons of many different sizes and reflectivity reveals enormously valuable data about (a) what our radar can and can't detect;  (b) what we're willing to do about it geo-politically and militarily;   (c) makes us prove how high an F22 can actually go;  (d) determines what kinds of targets a US air-to-air can successfully engage.  They learned a lot by simply flying a balloon over, period.

@MaxR Thank you! Please feel free to improve the answer or suggest edits.

@MaxR I don't assume anything, and I also don't put much credence in Stack Exchange comments. It seems that the "aw shucks, it's no big deal, just a single, lonely off-course weather balloon" narrative here is getting further and further from what's being reported https://www.nytimes.com/2023/02/08/us/politics/china-spy-balloons.html I'm beginning to think that the answer to "To what extent is modern "maneuverable spy balloonery" really a thing?" is going to turn out to be more like "Yes, it turns out in a pretty significant way!"

@PeterKämpf ditto

US National Security Council coordinator for strategic communications (and retired US Navy admiral) John Kirby: We knew for a fact that the (PRC) balloon that we shot down last week was, in fact, a surveillance asset and capable of surveillance over sensitive military sites and that it had self propulsion and maneuver capabilities. Either he chose a wrong word "propulsion" or he meant it, and having watched him talk for a while, as a spokesperson for the White House he seems to choose his words carefully. Size of solar panels seems key to propulsion.

https://i.sstatic.net/lbVjP.jpg from Top secret spy planes reveal details about China's spy balloon per Pentagon spokesperson Brig. Gen. Pat Ryder "I can assure you this was not for civilian purposes. That is, we are 100% clear about that." I'm still thinking that "to sell news and stoke irrational fear" is not a viable way to characterize the situation.

Mark Esper on the second flying object shot down over Alaska: But the other thing they have is persistence, so they can sit up there at 60, 65,000 feet with some degree of maneuverability and propulsion, and hover over a site in a way that an overhead satellite in space can not do.

Gen. Mark Milley: ...(at that) altitude those winds are very high; the particular motor on that aricraft can't go against those winds at that altitude... I'm going to conclude personally there was a motor with propellor(s) who's primary function was to rotate the craft around a vertical axis & point solar panels towards the Sun & perhaps point sensors and cameras as well, general attitude control around one axis. Such a system could also be used for gentle propulsion, but maneuverability if present came from altitude changes accessing winds directions.

to what extent is modern maneuverable spy balloonery really a thing?

While it is certainly debatable whether or not recent balloons in the news were maneuverable or not, technology does exist to attempt it.

Goal:  drift over Montana from around 10,000 km away

Montana is around 1000 km × 400 km.  Prevailing winds would favor a broad side approach.
Error margin: +/- 500 km.  $arc$ $sine$ (500/10000) = +/- 3 degrees.

check the weather before you go flying

Weather forecasting has grown in leaps and bounds in recent years, and world wide wind field maps are available.

moving with the air mass.

An all-time
Aviation Stack Exchange favorite.  Use buoyancy for lift, ride the wind.  This is exactly what this airship did during its 1929 round the world flight along a similar trans-Pacific route.  Knowing the weather helps.

maneuverability?

A 10,000 km trip at 100 km/hr will take 100 hours.  Gently moving in the airmass at 5 km/hour perpendicular to the ground speed would allow 500 km in either direction of manuverability.  Montana or bust!

is it really a thing?

It is technologically possible, but one can only ask that the science of this site not be dragged down into the political folly of the day.  Returning to 1929 may not be the best course, returning to 1914, worse still.

While the " +/- 3 degree" would make sense in the context of a ballistic trajectory, in fluid dynamics I don't think anything short of a simulation (some combination of Monde Carlo for the large-scale turbulence at boundaries and best available atmospheric model for the general wind directions vs altitude can address this. I agree that this site is Aviation SE and politics doesn't belong, thankfully I don't see it anywhere on this page. Anyway +1 and thanks!

For intelligence gathering a balloon would have a couple of advantages and several disadvantages. The disadvantages first. Limited maneuverability, most balloons can only float on the wind. You could add the ability to change altitude hoping to find winds blowing the direction you want to go. This leads to the second issue weight. To keep the size reasonable the mass of the payload must be limited. limited mass means things like large high resolution cameras are not feasible. this would include large motor for propulsion and equipment to change altitudes. Now for the advantages. They are much cheaper than satellites, high performance spy planes, or even drones. They are harder to detect. Ours defensive radar networks were simply not looking for them. Our radars were optimized to look for aircraft and missiles, not balloons. I assume that is being changed. Finally because we did not initially detect them we did not take any measures to "hide" ay activities. When I was in the USAF we knew when Soviet satellites were passing over head and made sure no aircraft were transmitting radar, radio, or ECM, and that all exterior panels were closed. We would sometimes even suspend work during the time they were overhead.

Wow, closing the exterior panels?  So the satellite couldn't see inside?

Correct, I never said what the military did made sense. The only thing I could see that they might learn is that a given plane was undergoing some type of repair.

@Jim or that it was or was not there or somewhere else at the time?

@uhoh Most air force bases were relatively small. You could typically view the flight line from roads just off base. It was not unusually to have people parks by fences to observe aircraft taking off and landing. Most simply wanted to see the planes. We had little doubt others were sending reports to the USSR. We never did, but some units would occasionally change the markings and even tail numbers to try and confuse them. The number of SR-71 and U2 aircraft were often incorrectly reported because of this.

@Jim yikes! It seems that times were a little different then :-)

authors: Vladimir F Героям слава


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Which airlines are banned from flying over Russia? Is there a list?
The New York Times' March 17, 2023 Banned From Russian Airspace, U.S. Airlines Look to Restrict Competitors includes the following:

On its route from New Delhi to New York City, American Airlines has been forced to stop flights in Bangor, Maine — an hour and a half short of the mark — on 19 occasions, a person familiar with the recent history said. Those stops, which were typically caused by unfavorable winds or weather that depleted the jet fuel supply and ran out the flight crew’s duty hours, delayed passengers and forced a swap-out of 14 pilots and flight attendants.
Those flights were already operating with dozens of the seats deliberately left unfilled, the person added, because less weight on board was required to make the fuel last as long as possible.
Yet many foreign airlines are not banned from flying over Russia, U.S. airlines and their lobbyists say — and are winning more passengers on routes to and from the United States as a result. Continued access to the shorter and more fuel-efficient routes that Russian airspace provides is giving carriers like Air India, Emirates and China Eastern Airlines an unfair advantage, the industry lobbying group Airlines for America said in a recent presentation on Capitol Hill.

and further down:

U.S. airlines for years had access to Russian airspace through a series of agreements with Moscow. In exchange for that access, they — and other foreign airlines — paid fees to the Russian government for air traffic control support that amounted to hundreds of millions of dollars per year, according to an airline official and an industry advocate.
But after Russia’s invasion of Ukraine last year prompted government officials in the United States, Britain, Canada and Europe to ban Russian aircraft from flying over their airspace, President Vladimir V. Putin of Russia immediately prohibited the United States and other supporters of Ukraine, including Canada and much of Europe, from flying through his skies.

Yet further down, the NYTimes article says

Representatives for Air India declined to comment, and representatives for Emirates and China Eastern did not respond to requests for comment.

Question: Which airlines are banned from flying over Russia? Is there a list?

different but potentially related What routes are available for airliners to fly from Europe to Japan without entering Russian airspace? and perhaps What is the altitude required to bypass Russia's airspace restrictions for airlines? and Is there a height limit to national airspace?

For those who are curious:  AA seems to currently be flying a DEL–JFK route that involves flying from Delhi to approximately Peshawar, turning due north until a point roughly due east of Dushanbe (thereby avoiding Afghanistan except for a brief crossing of the Wakhan Corridor), and then turning west and crossing the "stans", the Caspian, the Caucasus, and Turkey.

First of all, it should be noted that the Russian Federation is not a signatory to the International Air Services Transit Agreement (see list here), which would allow overflight according to the First Freedom of the air. Therefore, Russia does not have to ban specific airlines from overflight; it's rather the opposite: the airline needs to apply for an overfly permit. As far as I know, there is no public list of airlines that have an overflight permit or airlines where such an application for the permit has been declined.
Russia did react to the ban of Russian aircraft by issuing NOTAMs, which effectively do the opposite of these bans: they prohibit any overflight or other operation for aircraft that are in any way associated to one of the countries that banned Russian aircraft. You can search for these NOTAMs on the FAA NOTAM Search by entering UUUU as location. Here is an example for the United States:

U0609/22 NOTAMR U0606/22
Q) UUWV/QOAXX/IV/BO/A/000/999/5535N03716E999
A) UUUU B) 2205190000 C) PERM
E) AS A RESPONSE MEASURE TO THE DECISION
OF AVIATION AUTHORITIES OF THE UNITED STATES OF AMERICA AS TO ALL
RUSSIAN AIR CARRIERS AND COMMERCIAL AIRCRAFT OPERATORS, IRRESPECTIVE
OF REGISTRATION OF AIRCRAFT, ALL RUSSIAN AIRCRAFT REGISTERED IN THE
RUSSIAN FEDERATION, ALL STATE RUSSIAN AIRCRAFT, IRRESPECTIVE OF STATE
OF REGISTRATION OF AIRCRAFT, AND ALL ACFT IRRESPECTIVE OF STATE OF
REGISTRATION, OWNED, CHARTERED, RENTED OR OPERATED FOR OR FOR THE
INTERESTS OF RUSSIAN NATURAL PERSON OR ENTITY, STATED IN SUMMARY
CONSOLIDATED LIST OF THE UNITED STATES INTERNATIONAL STATE
ADMINISTRATION, AS PER NOTAM A0049/22, ARE PROHIBITED TO OPERATE
FLIGHTS TO, WITHIN, FROM OR VIA TERRITORIAL AIRSPACE OF THE USA, THE
AVIATION AUTHORITIES OF THE RUSSIAN FEDERATION HEREBY DECLARE THE
PROHIBITION OF OPERATIONS OF ALL AIRCRAFT, REGISTERED IN THE USA OR
OPERATED BY AIRCRAFT CARRIERS OF THE USA OR AFFILIATED WITH THE USA,
ALL TYPE BOEING 737MAX AIRCRAFT, IRRESPECTIVE OF STATE OF REGISTRATION
OR STATE OF OPERATION, WITHIN OR VIA AIRSPACE OF THE RUSSIAN
FEDERATION, INCLUDING TRANS-SIBERIAN AND CROSS-POLAR ROUTE SYSTEM
(TRANSIT) FROM 0000 UTC 17 MAY 2022, EXCEPT EMERGENCY, HUMANITARIAN,
SANITARIAN FLIGHTS  AND FLIGHTS WHEN SPECIAL PERMISSION FOR OPERATION
OF SUCH FLIGHTS IS GRANTED BY THE FEDERAL AIR TRANSPORT AGENCY OF
RUSSIA OR THE MINISTRY OF FOREIGN AFFAIRS OF THE RUSSIAN FEDERATION,
AS APPROPRIATE.

(emphasis mine)
There is a list of countries and the associated NOTAMs on makgas.com, which claims to be updated regularly (I haven't checked). The current list of countries and territories, which are banned, is:
Albania, Anguilla, Austria,
Belgium, Bermuda, Canada,
Croatia, Cyprus, Czech Republic,
Denmark, Estonia, Finland,
France, Germany, Gibraltar,
Greece, Hungary, Iceland,
Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta,
Montenegro, Netherlands, North Macedonia,
Norway, Poland, Portugal,
Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland,
Turks and Caicos, United Kingdom, USA

They also have a map with these countries on the site:

(makgas.com)

What the heck is a "SANITARIAN FLIGHT"? (Had to read it 3 times before I realized it wasn't "Sanitation Flight"...)

@FreeMan:  Probably a mistranslation of "sanitary flight", which is another phrase for a medical transport flight.  Someone who knows Russian better than I do might comment on whether such a phrase is common in Russian.

source: Stack Exchange

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sort: votes


text:
Nutritional value of jet fuel (from a microbe's point of view) and which of their byproducts is causing the fuel tank corrosion?
Self-described "pilot, aerospace engineer, and mad scientist" YouTuber Jack Schneider's video Growing Microbes in Jet Fuel explains that if a layer of water accumulates below jet fuel (due to separation or perhaps other reasons) microbes (bacteria, algae...) can grow in the water and "eat" the fuel:

...since water is denser than jet fuel it sinks to the bottom and creates a layer where microbes can form. Basically the microbes can eat the jet fuel but live in the water and I think that's really interesting. This is a problem in jet fuel tanks because these microbes' byproducts can cause corrosion.

Question: From a microbe's point of view, besides the calorie content of the carbohydrates (hydrocarbons) what are the trace components of jet fuel from which microbes derive nutritional value, and which of their byproducts is causing the fuel tank corrosion?
Just for example: life is based on proteins made of amino acids, and two of these (Methionine and Cysteine) have a sulfur atom. The human body for example (though not a microorganism) is 0.3 % sulfur by weight. So a 70 kg body has about 11 kg of protein, and 200 grams of that is sulfur!
This answer to Why is water-contaminated fuel bad, but water-injection is not? mentions

Water not removed from the tank supports microbial growth.

and this answer to Why aren't "fuel polishing" systems removing water & ice from fuel in aircraft, like in cruising yachts? mentions

...you have ideal conditions for the growth of microbial life in the fuel. This life (technically known as "goo") will, if left to grow rampant, clog your filters to the point where the engine eventually shuts down from lack of fuel.

But neither mention nutritional details nor corrosion.

Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed.

The question is complex and really not really aviation-specific. Cars, trucks and especially boats and ships have similar problems.
The energy content of the fuel is well-known and some microorganisms really do have the enzymes to break it down, at least partially.
On the other hand, it is usually not the sulfur what limits the bacterial growth there. Jet fuel contains  ~500 to 1000 ppm sulfur. I am sure I (and I am not the only one) have dealt with a diesel tank that had bacteria while sulfur in EU diesel was less than 50ppm for years.
The limiting factors of any life (if the energy is abundant) are usually nitrogen and phosphorus. In contrast with sulfur, these are not considered pollutants and their presence in the fuel is not carefully managed, so bacteria usually have enough of both in the tank.
The inevitable contaminants in the fuel bring the needed microelements.
It looks like the limiting factors for bacterial growth in a fuel tank are the temperature (sub-freezing is not OK for any bacteria) and the limited surface of the water/fuel interface (bacteria needs both and they don't mix) and the availability of oxygen at the interface (usually at the bottom of the tank).
The scarcity of oxygen where these bacteria grow means that their byproduct will be mainly a mix of carboxylic acids (this is how we force some other bacteria to make pickled cucumbers or vinegar for us).
And this is what promotes the corrosion in metals.

Thanks for your answer - the most helpful bits seem to be right at the end. As far as "(c)ars, trucks and especially boats and ships have similar problems" goes, they can also have serious problems with ice buildup on the windshields in adverse weather conditions, but that doesn't make questions about what causes and seeds, and what prevents icing any less interesting for Aviation.

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text:
How common is the use of "quick-set asphalt" on runways such that flights may begin just a few hours after paving?
In the DCist's August 8, 2023 At DCA, Crews Race Each Night To Repave A Bit Of Runway Before The Next Day’s Flights they describe how runway repaving at Ronald Reagan Washington National Airport (DCA) is being done.
From what I gather from the text below, each night starting promptly at 00:00 a section is dug up (top 8 inches removed) and between 01:00 and 03:00 the section is repaved with "quick-set asphalt" such that at only a few hours later at 06:00 the first flights are using the new asphalt.
Question: How common is the use of "quick-set asphalt" on runways such that flights may begin just a few hours after paving?
There must be an awful lot of checking and inspecting going on between 03:00 and 06:00 such that the new runway section is qualified for unlimited use (big heavy planes, potentially hard landings) each morning. Is this a one-of-a-kind situation or more common than I'd realized?

11:57 p.m.: It is just minutes before midnight and a series of American Airlines planes are taking off in quick succession before the deadline. The last plane takes off just seconds before the clock hits midnight and the calendar turns over to July 17.
“This is whisky 4-7, are we clear to get in?” a worker asks into a handheld radio.
“(Secondary runway) 15/33 is now closed,” an air traffic controller responds. “I repeat 15/33 is now closed. You can now proceed onto 15/33.”
Even before the air traffic controller finishes his sentence, dozens of trucks, semis, and other equipment are off to the races, speeding ahead to the work site. The much slower brontosaurus-looking milling machines follow slowly behind.
[...]
12:15 a.m.: The specialized milling machines get to work cutting eight inches deep in one swoop. They’ll do a 15-foot wide stretch about three football fields long in an hour.
When they’re done, they leave rough pavement in their wake. Then, crews lay hot asphalt and roll it flat, which takes about two hours.
So how do planes land the next morning without getting sticky tar on them? It’s because crews use quick-set asphalt and only do small portions of the runway at a time.
[...]
The next morning we learn the crew beat the clock: A United flight to Newark took off at 6 a.m. on the dot that morning. It’s another night well-orchestrated, and they’ll do it all over again tomorrow. It’s the latest in a line of triumphs; workers haven’t missed a deadline yet.

Sounds horrifyingly expensive.

@Chris Yes, no doubt. Wikipedia's Ronald Reagan Washington National Airport says "It is the smaller of two airports owned by the federal government and operated by the Metropolitan Washington Airports Authority (MWAA) that serve the Washington metropolitan area around Washington, D.C.; the larger is Dulles International Airport" which is further away from DC. So I don't think the focus is on maximizing short-term profit; From the Government's point of view it's simply essential.

@Chris and the US government is certainly no stranger to "horrifyingly expensive" endeavors.

Horrifyingly expensive compared to what? Doing the work more slowly during the daytime would be horrifyingly expensive if the airport lost revenue because they had to reduce capacity or close while the work was completed.

@Chris  Doesn't sound that expensive to me - maybe double the cost of doing it all in one go, in daylight? (Men working 2/3 of a full shift , but on slightly higher pay rates.)

@MikeB Think of the overhead of getting ready for the day's shift and finishing up to reopen the runway. That's all time you're paying people and using equipment and no runway is being replaced.

Apparently this isn't just common, but appears on its way to becoming a standard practice. London's Gatwick Airport (LGW) recently redid its main runway (they have a shorter and narrower standby runway only used in situations like this) and they used asphalt as well (paving portion starts around 7:39 in the video)

Gatwick actually staged a temporary on-site asphalt batching system and laid new sections in two layers done in one night

This highly innovative approach moved away from the traditional method where sections of the old runway surface is replaced with two layers, laid over two nights. Instead, a resurfacing technique was developed that saw both layers laid in a single night – saving time.

As with DCA, the runway was in use by the next morning


text:
When did "the US presidential plane" land on Diego Garcia for refueling, and which if any president was on board? (circa 2000's)

Source: BBC
I am uncertain if this is a question for History SE or Aviation SE; I've decided to try here first.
I was reading the BBC News's September 29, 2024 What I found on the secretive tropical island they don't want you to see about Diego Garcia (see also Naval Support Facility Diego Garcia)

During my time on the island, I am required to wear a red visitor pass and am closely monitored at all times. My accommodation is guarded 24-hours-a-day and the men outside make a note of when I leave and return - always under escort.
In the mid-1980s, British journalist Simon Winchester pretended his boat had run into trouble next to the island. He remained in the bay for about two days, and managed to briefly step on shore before being escorted away and told: “Go away and don’t come back.”
He tells me he remembers British authorities there being “incredibly hostile” and the island as “extraordinarily beautiful”. More than two decades later, a Time magazine journalist spent 90 minutes or so on the island when the US presidential plane stopped there to refuel.

If there were reporters on "the US presidential plane" then there's a pretty good chance there was a president on board as well. Which piqued my curiosity.
Question: When did "the US presidential plane" land on Diego Garcia for refueling, and which if any president was on board? (circa 2000's)
"bonus points" to help me understand if this was a notable occurrence, or if it turns out to be routine (except for the reporter getting off).

See also in Space Exploration SE How was an emergency landing site at Diego Garcia used during the Apollo program? (which includes a video clip of the Diego Garcia airstrip from a satellite) where there are mentions of Diego Garcia in the context of both the Apollo missions and the Space Shuttle.

I found this picture of the U.S. presidential plane at Diego Garcia, taken by Mass Communication Specialist Seaman Jonathen E. Davis:

Source: naval-technology.com
The description tells us:

Diego Garcia's executive staff including Naval Support Facility Diego Garcia's Commanding Officer Capt. Greg L. Looney and British Representative Cmdr. Gary Brooks salute Air Force One as it taxis to a stop.

Another photo by the same photographer can be found on wikimedia:

The description tells us that on september 4, 2007 :

President George W. Bush and Capt. Greg L. Looney, commanding officer of Naval Support Facility Diego Garcia, inspect military members on the flight line during the president's recent stop in Diego Garcia. President Bush stopped on the island en route to Sydney, Australia, for the Asia-Pacific Economic Co-operation forum.

Putting this together I suspect that this is the flight you are referring to.

Shortly after this answer was posted, @mins found the article in Time magazine

... We were taken to an auditorium while Bush met the base commander and troops elsewhere on the grounds.

This is consistent with the information above.
A globalsecurity.org article found by @mins explains:

This was Bush’s first visit to Diego Garcia and the first visit from any U.S. president in quite some time.

This confirms that it was a notable occurrence for a U.S. President to visit Diego Garcia.

"President George W. Bush and Air Force One during a ninety-minute
refueling stop between Iraq and Australia." - Page 7, Introduction
Note: The book describes how the island was taken from the native Chagossian people and ruined many of their lives.
Source:
https://www.amazon.com/Island-Shame-Secret-History-Military/dp/0691149836

It is likely that there were several stops or visits, it is a very important base and the period being considered is long.

authors: Vladimir F Героям слава


text:
NASA's flying telescope SOFIA — How to find flight plans and real time location?
SOFIA, NASA's Stratospheric Observatory for Infrared Astronomy:

SOFIA is based on a Boeing 747SP wide-body aircraft that has been modified to include a large door in the aft fuselage that can be opened in flight to allow a 2.5 m (8.2 ft) diameter reflecting telescope access to the sky. This telescope is designed for infrared astronomy observations in the stratosphere at altitudes of about 12 kilometres (41,000 ft). SOFIA's flight capability allows it to rise above almost all of the water vapor in the Earth's atmosphere, which blocks some infrared wavelengths from reaching the ground. At the aircraft's cruising altitude, 85% of the full infrared range will be available. The aircraft can also travel to almost any point on the Earth's surface, allowing observation from the northern and southern hemispheres.

has arrived in Christchurch New Zealand for a period of airborne observations; 1, 2. More about SOFIA can be found at SOFIA Science Center official website.
I know that there were plans to try to observe a rare occultation event, where the asteroid 2014 MU69 around 17-July 2017 will pass in front of a faint star and block out its light. There are predictions (data and maps) shown below, and a cryptic list of SOFIA flight plans can be found here.
You can read more about what's happening in this interesting answer as well as in the original question there. This is important because 2014 MU69 is the next target for the New Horizons spacecraft after its Pluto flyby in July of 2015.
QUESTION: If I wanted to look for official flight plans, and watch for any possibility of near real-time data (even if intermittent) on FR24, how and where could I look up the SOFIA aircraft?

above: predictions from here.
below x2: images from Space.com's Photos from SOFIA, NASA's Flying Telescope (Gallery); click them for full size images.

I don't know where to find flight plans, but according to Wikipedia, the aircraft is a Boeing 747SP with registration NASA747.
"747SP" set as aircraft type filter in flightradar24 was enough to find SOPHIA right now :

OK SOPHIA is on the move now. Since the astronomically interesting part of the flights may be over open ocean, the FR24 historical data will probably have large missing sections. But that will just make the interpretation more interesting to piece together. It's possible the filed flight plans are not publicly available, or that they might not contain enough specific information to correlate with astronomical observations. So this is really all I need to get started at least, thanks!

It's hard to tell visually, but it doesn't look like it made it into the predicted path of 2014 MU69's occultation today. Will check more carefully later. https://i.sstatic.net/BWtXf.png

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Are an aircraft's nuts and bolts generally either all Imperial or all Metric, or can they be mixed?
This is a low-tech question, but I was wondering about the distribution of imperial vs metric hardware on aircraft.
When current commercial aircraft land at major airports, a mechanic will know which set of wrenches to grab. Still, I wonder is everything metric, or are some commercial aircraft still imperial? Could an engine or some subsystem use one kind of hardware on a plane that mostly uses the other?
What about at a more remote airport visited by a wider variety and vintage of aircraft? Would a mechanic need to go up and check before deciding which toolbox to use?

Found in this comment under this answer

Similar question: Are there differences in tool standards between aircraft manufacturers?

The vast majority of civilian aircraft and powerplants flying worldwide are manufactured in the USA or Canada using almost exclusively Standard hardware, usually conforming to aircraft Mil Spec (MS) or AN specifications. From that perspective, the answer to your question is that any given aircraft will most likely use all Standard hardware.
This is even true for some European built aircraft such as the Reims F172 manufactured in France, or the Italian SIAI Marchetti F260. These aircraft use standard hardware, such as AN bolts and washers.
As Peter Kämpf described, there certainly are aircraft with a combination of hardware types. There are also a significant minority of aircraft that use exclusively metric hardware.
In any event, maintenance personnel will often have documentation detailing the exact type of hardware used on the airframe and engines. Older aircraft may not have this documentation, for example for a Beech Staggerwing, but the vast majority of such aircraft will use Standard hardware.
Most aircraft mechanics do not have any metric tools in their aviation toolboxes. There will be an exception, obviously, for those that do work on the minority of aircraft with metric hardware.
Speaking from my experience of having worked at remote airports, on vintage aircraft, most toolboxes reflect the use of Standard hardware. The metric box is typically reserved for use on automotive projects. That does not mean there are no exceptions; there are.

You have never looked into the toolbox of Russian aircraft mechanics, have you? They all have exclusively metric stuff.

@PeterKämpf No, I haven't, and my answer allows for that. The question asks about generalities, and I have answered in generalities.

@PeterKämpf presumably they don't use it on non-metric aircraft. Oh, do you mean aircraft mechanics who are Russian, or mechanics of Russian aircraft?

@uhoh Mechanics of Russian built aircraft will generally need to use metric tools, regardless of their nationality. Russian mechanics will need to select their toolsets based on the aircraft they are working on.

This is exactly the kind of answer I was looking for, but I was quite surprised by the actual answer. Thanks! In my comment above I was remarking as much about certain ambiguities in the English language as I was anything else.

Can you include what 'AN' stands for?

@TomMcW AN used to mean Army/Navy or Air-Force/Navy, depending on who you ask. I believe the term has outgrown the old acronym, but others might tell you otherwise. National Aerospace Standards (NAS) is another designation used for hardware.

Why not mixed? If the airframe is manufactured in a "metric" country but the engine is from the US, you will find metric nuts and bolts behind the firewall (and on the engine mount) but Imperial on the engine.
If I remember correctly, the Robin DR-300 and DR-400 that towed me many times had just that mixture. Lycoming engine and French airframe.

You probably mean the Robin aircraft, not the similar Jodel.

@JonathanWalters You're right. We always called them Jodel.

We work with (Czech Made) Aircraft Industries Aircraft and they still use the Metric Systems.

"metric hardware" or "metric tools" right? Metric system sounds more like altitude in meters, speeds in kph.

yes our nuts and spanners are in mm and not in inch

In a nut shell, all measurements are moving to metric so older air craft like the C-130 is all in feet and inches and weights are in kgs. So the trim sheet has to be converted to this. However the newer aircraft like the C-17 and aA-400 are in lbs and meters and again anything loaded has to be converted to the trim sheets. To be honest its not hard to convert between the different airframes.
The Concorde was made using both metric and imperial as it was a joint British-French build. It all fit together perfectly.

Thanks, but please re-read the title and first sentence of the question. Hardware. Nuts and bolts.

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Is it possible to take off on an elevated short field by "falling"?
I understand this may be a dumb question to ask, but - in the opening sequence of Golden Eye - James Bond chases after a plane that has rolled off the side of a cliff in his motorcycle, and then somehow (movie magic) climbs into it and pilots it away.
I am not asking about the physics of the motorcycle stunt - except keeping it to the aircraft part:
Is this something that can happen in real life - that is, an elevated airfield so short, that the plane has to "fall" to obtain enough speed to gain lift?
Has something like this ever been attempted, even if simply as an exercise in flight dynamics?

Perhaps a more realistic scenario would be launching a plane from an airship.

Does your question presupose the initial absence of a pilot, as in the Bond sequence, or does your question allow for a piloted "fall" takeoff? If the first, the answer is probably no, if the latter, yes. The answers so far presume one or the other, but this isn't clearly stated.

There are birds - fulmars and probably albatrosses - that cannot take off from flat ground. (Or flat water in the absence of wind and waves) They nest on high cliff ledges and this is their normal mode of takeoff. Imagine the chicks who have one chance to learn to fly!

@JonathanWalters I meant with a pilot in command and not superman-ing their way into the cockpit like everyone's favorite spy.

Pilots, if I'm not mistaken hang-gliders do this every single time, right? It's more a matter of scale. For a hang-glider you need only a small amount of forward speed to achieve this, and then use the added speed of the fall to achieve flight.  For a large aircraft, you'd need more "starter speed" to make it work, and not just messily tumble in to the cliff. That seems to be all there is to it.

I've actually sort of done it.  Stead airport (near Reno), hot day, overweight flying instructor (and me at ~190 lbs) in a tired Cessna 150.  At the east end of the runway there's a sharp drop (not quite a cliff) down to a dry lake.  So do takeoff run, and get airborne in ground effect, pass over the end of the runway, and look back to see that we're actually below it.

There is footage of exactly this in the film Only Angels have Wings (1939).

@tas Or another real-world use would be a carrier-bourne launching catapault for launching planes, where the push makes up for the lack of space to drop.

They also do it multiple times in the movie 2012, and one time its with an Antonov 225!

Is jumping into the "movie magic"? No: a stuntman actually did it for the movie cameras! Sure he was a professional skydiver with a wingsuit, a pilot was in the plane flying it at the slowest possible speed, cabin was prepared to have something to grasp inside and avoid being hurt when entering, but he actually flew into the plane!

Is it theoretically possible? Sure.
Is it realistic or probable? Absolutely not.

If there is not enough space for the airplane to accelerate to takeoff speed it will be effectively stalled when it reaches the end of the ground. That means that as soon as it runs out of ground it effectively becomes a ballistic projectile: it keeps moving forward, but it also starts to fall because of gravity. You can see this in the Goldeneye clip - the plane adopts a nose-down attitude shortly after it leaves the ground.
Eventually, given enough time, the airplane will reach a flyable airspeed (between gravity accelerating it down and its thrust propelling it forward). How far it needs to fall before that happens depends on a number of factors, but if the ground is sloping downward at an angle such that the aircraft's ballistic trajectory does not intersect the ground before it can reach flying speed you could theoretically make such a takeoff.
The obvious downside is that if things don't go perfectly in the attempt you will intersect the ground in uncontrolled flight ("crash").

In the Goldeneye scenario the aircraft is already in a fairly extreme dive when Bond manages to get aboard, so for our intrepid secret agent it's not so much a matter of getting the aircraft to a flying speed (it's probably there already) but rather of recovering from the dive before hitting the ground and without over-stressing the airframe and causing parts to break off.

"You will not go to space today"

Isn't flying off a cliff and only gaining sufficient airspeed to remain in flight afterwards what fixed wing aviators on sky-jump style carriers do every time they take off?  OTOH every part of what naval aviators do could be called insane I suppose.

I think there can be a phase when wing isn't stalled already, yet still not generating enough lift to support all the weight. https://www.youtube.com/watch?v=cWOcRl2Q1T4&t=2m00s Depends on the plane, I guess, but seems like all hang gliders are designed for that.

This is a great post, but it's not just a matter of speed - taking off into a headwind can also add lift to the aircraft and affect the outcome by increasing the rate of airflow over the airfoil on the wing.

When no lift is being produced, the wings will not stall (0-g maneuver)

@DanNeely Yeah, with the caveat that the "ski jump" ramp also aims them nose-up (so their velocity vector has some "up" component to it when they come off the end). It's also what gliders/hang gliders do when you launch them by jumping off a cliff. (They're relying on other things too, like ridge lift, which I'm neglecting in my analysis because they're less significant for heavier powered airplanes, but the principle is the same: Fall until you have airspeed, then fly!)

@Agent_L Generating some lift but not enough to support all the weight is called "descending".

I'm taking that you mean taking off (for the want of a better word) when the runway is unavailable- trade altitude for gaining speed and get back to controlled flight. This is certainly possible but not recommended as it puts too much premium on pilot skill and luck.
There are videos in the internet which shows exactly this being done, but whether anyone would want to try this is questionable. Atleast this shows that as long as the aircraft is kept clear of the ground below for a reasonable amount of time and the aircraft does not stall, the aircraft could be flown off the cliff.
Another way of looking at this is to consider the experiments carried out in 1930s with airships and 1950s with large bombers, which launced aircraft from an altitude.
The McDonnel Douglass XF 85 Goblin was purpose built to be carried and launched from bombers; the launches were successful, the trouble was with the retrieval of the aircraft. The advent of the air-to-air refueling put and end to the experiments.

Yes, an airplane can be launched by gravity acceleration, whether by a short takeoff run, or actual free fall. As other answers have indicated, there are many instances of this taking place from short runways or hillsides.
An obscure application of this ability is found in the curious history of the Curtiss Sparrowhawk, a "parasite fighter" that launched from US Navy airships. The aircraft was stored in the airship, which was a sort of flying aircraft carrier. To launch, the Sparrowhawk was lowered below the airship by the hook above the wings, the engine was powered up, and the aircraft was released to fall away and gain airspeed.

[Source, public domain]
Video the USS Akron showing Sparrowhawk launch (launch sequence starts at 1:40)

Interestingly, the Sparrowhawk used the launch mechanism for retrieval into the airship. Read more about the Curtiss F9C Sparrowhawk, and the two airships that carried it, the USS Akron and the USS Macon on their Wikipedia pages.

I wouldn't think this actually qualifies as a "takeoff on an elevated short field". Interesting, still.

@StéphaneGourichon You are correct that the sparrowhawk example does not involve a field at all. The point of that example is to illustrate that a freefall is sufficient to accelerate an aircraft into flight.

@StéphaneGourichon Technically, it is elevated and the field length is 0 feet, which seems very short. :)

But the Sparrowhawk would already have the airspeed of the carrying aircraft, so it doesn't have to accelerate much more, does it?

It sure is possible, and sure has happened!
Check out this video. Looks like a whole lot of fun. As long as there is enough forward trajectory to clear the edge, and enough room before the ground, it can be done. I wouldn't like your chances of pulling it off in a larger aircraft however, and the piloting technique would need to be precise.

You have to consider that this plane you showed takes off in probably something like... 100 ft?

@Nelson At 6:00 in that video, he seems to take off in even less than that!

That plane is definitely an exception.  It's a twin propeller designed so that it can even take off on only one engine.

The fact that this is a taildragger may also be relevant. It means the pilot is already actively balancing the aircraft pitch during the takeoff run. He probably has to make a massive correction as it goes over the cliff, but at least he has some feedback. The plane in Goldeneye is also a taildragger, and a stuntman presumably did have to more or less fly the plane off a cliff in order to get the footage.

The propeller visible at the top of the video may suggest that it's a helicopter, but the link on the video shows a photo and it's indeed a plane: http://www.bushplanedesign.com/

One of the greatest books on aviation ever written, Fate is the Hunter by Ernest K. Gann, has a story about departing Africa fully loaded with fuel off of a river in a seaplane, and they couldn't get airbore before the river turned into a waterfall. When they reached the waterfall, they lowered the nose until they reached flying airspeed, and flew away. It wasn't planned, but they made it anyway.  So, yes, it is possible. And run, don't walk, to your favorite bookstore and buy this book. I read it every year.

Now I'm remembering something about the wings being overloaded with fuel and pinching a cable so they couldn't rotate until they were airborne.  Does any one have a better recollection?

Ah, good story. While we are on the aviation books, nobody won't regret to read St Ex Wind, Sand and Stars and re-discover what has been the life of aviation pioneers. So humanist.

I'm surprised to see Courchevel Altiport being only mentioned in comments in this question. While this is not exactly a free fall, the middle part of the runway has a significant slope (18%), which contributes toward accelerating the planes taking off (as well as slowing down the landing planes).

One similarity with a free fall is that once the plane reaches the slope, the pilot cannot do RTO anymore, because of a short remaining distance and additional acceleration from the slope:

And that’s where we come to the ‘dilemma’ on this runway. Once the DASH 7 has started moving there, there’s no turning back: it just has to take off. Aborting a take-off on a runway this steep is absolutely unthinkable. We could no longer bring the aircraft to a standstill, and I don’t even want to think about the consequences of that…

I think that it was contained to comments because it does not actually answer the question.

Well, there's still gravity contributing towards accelerating the plane.

Can a glider take off from there? If not, it's not really an answer to the Q.

Short answer: yes, but...
There are already a number of good answers and examples that, while unprobable (in the sense of "requiring a specific combination of factors") and dangerous in most of the cases, it is definitely really possible (since it happened).
Adding an historical example
At the beginning of commercial aviation, unreliable planes carried paper mail (a.k.a. post, letters) in daredevil conditions.
In between 1927 and 1929, Jean Mermoz was trying to open a route across the Andes. He and his mechanic stranded at high altitude after an incident, rode into a precipice to gain enough speed to fly again.  This has been widely documented for decades.
See for example:
Jean Mermoz (1901 - 1936) - SP's Aviation

He rode an updraft that carried the plane through a high mountain
  pass, but then a downdraft slammed the aircraft onto a plateau at
  12,000 feet. Though the small machine suffered only mild damage and
  was still airworthy, there wasn’t enough take-off run available on the
  plateau. Mermoz cleared a rough path to the edge of the precipice and
  they removed whatever they could from the aircraft. They strapped
  themselves in and Mermoz just rolled off the mountain hoping to gain
  enough flying speed before hitting the ground. They succeeded;
  otherwise it would have been certain death.

Famous Aviators | 10 famous aviators

Mermoz next tackled shortening the Argentina-to-Chile route; pilots had to make a thousand-mile detour to get around the Andes. With mechanic Alexandre Collenot, Mermoz set out in a Latécoère 25 monoplane and found an updraft that carried them through a mountain pass, but a downdraft smashed the aircraft onto a plateau at 12,000 feet. After determining that they could not hike out, Mermoz cleared a crude path to the edge of the precipice and removed from the aircraft anything that wasn’t bolted down. He and Collenot strapped themselves in, and Mermoz got the airplane rolling down the path.
In effect, they dove off the mountain, and Mermoz pointed the nose straight down, hoping to gain flying speed. Again, luck was with him.

voretaq7's answer seems to explain quite well what's going on but I suggest taking a look at the 'bungee launching' of gliders/sailplanes. Effectively the aircraft is initially accelerated by an elastic band, and then gains airspeed by falling down from a hill, almost exactly as you ask.
It is still is used at 2 places in the UK occasionally. The hill must be 'right' for it to work.
So yes, this does actually happen in real life, but not with 'normal' (powered) aircraft.

To add, at Camphill airfield and a site in Kent in the UK.

Some British aircraft carriers have ski-jumps at the end of their flight decks.  These allow aircraft that are rolling forward already (but too slow to sustain flight) to convert some of their forward velocity into vertical speed, in effect "lobbing" them into the air.
Obviously if their engines were not providing thrust, they would soon get wet, but it would take longer to hit the water than if they had just rolled off a flat deck.  This gives the aircraft extra time to accelerate to the speed required to sustain flight, and allows a shorter flight deck (so smaller ship, which means cheaper)
Depending on your frame of reference, you could say that the aircraft "fall" of the end of the ski jump.  They certainly have a negative vertical acceleration for a small amount of time, until the airspeed is high enough for the wings to totally counter gravity.
https://en.wikipedia.org/wiki/Flight_deck#Ski-jump_ramp

IIRC the ski-jump followed on from some WWII operations in which dropping off the end of a flat deck was sued -- whether this was by design or in emergency I don't know.

@ChrisH, If I was told to simply accelerate until I ran out of deck, then hope for the best, I would probably sue, too!  :)

The book Hitler's Raid to Save Mussolini by Greg Annussek (page 6, second to last paragraph) discusses the rescue of Mussolini; they used a 200 meter runup then off a cliff in a Storch.

To be fair, I've seen a Storch in person accelerate from inside a hangar in and be in the air by the time it was out of the hangar doors. It's more of a kite than an airplane.

I see no reason why it should not be possible if you have enough speed to clear the cliff and keep the nose pointed into the relative wind. In this 0 g maneuver the wings will not stall as long as no lift is being generated. If there is sufficient clearance to gain enough speed to reach a flyable speed and pull up before hitting the ground, it should be ok (not considering practicality).
Make a good paper airplane and drop it forward-end facing down, it will fly without a problem (if you made the plane properly)


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What can ground personnel do in the event of in-flight depressurization?
If the pilots, crew and passengers had all passed out from an unexplained result of gradual de-pressurization, and ground personnel were somehow aware of this scenario, would there have been anything that could of been done to save the plane and people before the fuel ran out?

No.  If the crew and passengers have all passed out due to lack of oxygen and the plane has not been commanded for a descent, they will never wake up.  This has happened before, e.g. the Payne Stewart fatal accident.  In cruise flight an autopilot is only commanded to perform lateral navigation and absent instructions from the crew to initiate a descent it will fly to its last fix and then maintain its current heading, all the while maintaining altitude.  When fuel is exhausted it will maintain altitude at the expense of airspeed until the stick shaker activates, disconnecting the autopilot.  Absent the pilots input, the stick pusher should next activate to forcefully prevent a stall.  You'll probably get some oscillations in pitch but ultimately a steep descent that even if the (literally) brain dead crew could somehow wake would not give them time to act.
While ground crews can get data from the airplane and can attempt to contact the crew, they cannot remotely control the airplane so the best they could do, if aware, is watch.  They could perhaps get a fighter scrambles to intercept and visually inspect the cockpit, but that still would not allow them to alter the outcome (just verify the scenario).
Note that this scenario is much more likely to happen in an extreme depressurization event in which the crew is unable to don O2 masks in time.  A slow gradual depressurization will give plenty of warning as the cabin begins to climb and automated sensors start complaining.  In the EMB-145 you'll start getting aural warnings when the cabin exceeds 10,000 ft pressure altitude and somewhere shortly above that you'll get master caution alarms and automatic pax 02 deployment.  These altitudes should give the crew ample warning before becoming hypoxic (you can reach these altitudes for limited time with no supplemental O2 in a Cessna 172 for example).  Even at cruise, it only takes a few minutes to get the plane back down to 10,000 ft and as such a slow gradual depressurization should not pose a threat unless multiple warning systems are malfunctioning.

You beat me to the Payne Stewart example by three minutes.

I'd be more worried about a slow depressurization event than a fast one.  If the roof of the airplane rips off or something, your blood is still fully oxygenated and you know what to do with the mask hanging in front of you.  With a slow depressurization, your blood will be deoxygenated to the 12000-foot level, your thinking will be foggy around the edges, and there's a risk you'll be fixated on a task and ignore your mask for too long.

Another example is Helios 522 a 737 with incorrect pressurization settings that flew for several hours with an unconscious crew before crashing. A flight attendant eventually gained access to the cockpit just as fuel ran out.

@Mark I still don't buy it. An extreme depressurization may start off with oxygenated blood but you may only have 30 seconds to react. With a slow depressurization you have to listen to audible warnings, master warnings, ignore EICAS information for however long it takes to become hypoxic before it is too late. The plane I'm familiar with will start yelling at you at 10000 ft cabin altitude. You have a much longer window of opportunity to act in the slow leak case.

As an aside, one of the first effects of hypoxia is that you start to lose reasoning and ability to recognise that you actually are hypoxic.  In controlled tests, aircrew can be well beyond the point of recovering the situation without even realising that they have a problem. There's an interesting video on YouTube somewhere of an ATC recording of a pilot suffering from hypoxia and being talked down to a lower level.  He very quickly regained full focus with no il effects.  If I can find it, I'll come back with a link.

http://www.youtube.com/watch?v=_IqWal_EmBg

@casey: Just go and look up report of the Helios 522. They had warning, didn't recognize it, even called dispatch, but by the time maintenance realized what the warning was, the pilots were too confused to carry out the instructions.

@JanHudec In that accident I see 3 chain links that were critical to that accident 1) Mx improperly resetting the pressurization 2) The crew failing to properly perform their receiving checklist and 3) misinterpretation of the EICAS warnings around 12,000 ft.  This led to hypoxia but I put this one on the crew.  I'm not familiar enough with the 737 and perhaps it is any easy mistake to make.  I draw all my experience from the EMB-145, and in that airplane it would be hard to make the same mistake with the warning systems that are in place.

@casey: The point is that the third failure shows how hypoxia sets in. Yes, gradual loss of pressure actually happens rather often (there are several such incidents every year) and pilots handle them just fine. It is also much less likely to do the same mistake in an aircraft with full glass cockpit which can describe the problem in detail; Helios 522 was a 737-300, which still had classical panel of warning lights.

@casey, given my recent experience with trying to perform two simultaneous tasks (drive a car and describe my surroundings) at 11,000 feet, I wouldn't count on being able to react to a slow leak.  Lack of a dashcam means I don't know what happened to my driving skills, but my voice notes were certainly a mess.  (Incidentally, does anyone know where I can get a supplemental-oxygen system for a car?)


text:
QF72: How could a disconnected autopilot change the pitch?
So I was reading about flight QF72, where the A330 had incorrect sensor data. The aircraft automatically pitched the nose down twice in response to abnormally high incorrect angle of attack data, but it did so AFTER the autopilot was disengaged. (See https://www.atsb.gov.au/media/51218/AO2008070_interim.pdf page 16-17).
How is that possible? Isn't it the autopilot that does that? I am probably getting the wrong idea about what the autopilot does, right?
Also, what would be the idea behind why the pilots attempt to correct the situation by pulling back the sidestick be unsuccessful at first, but suddenly have the desired effect right after he stopped giving that input?

The A330 has a degree of automation that can't be turned off, as part of its 'fly by wire' system.
This is to say that the pilot's controls aren't directly connected to the control surfaces. They are electronic in nature, sending signals to a controller which then decides how much to move the control surfaces.
As part of that, an automatic feature is built in to prevent the aircraft from entering flight attitudes that could be dangerous. This safeguard detects unsafe flying conditions using input from the the Air Data Inertial Reference Unit (ADIRU).
In the QF 72 case, a fault in the #1 ADIRU led it to believe that the aircraft was in a 50 degree nose up attitude, so it automatically forced the nose down. Problem was... the aircraft was flying straight and level, so the result was a very sharp nose down attitude, with negative G's applied to to the cabin (and everyone in it). Anyone not strapped in was slammed into the ceiling, and then into the floor when QF72 recovered from the dive. (only to do it again)
In this case, it wasn't a faulty AOA sensor, but a faulty ADIRU, which appears to have hit an unforeseen combination of inputs... and an unfortunate combination of data and timing that led the Flight Control Primary Computer that actually runs the control surfaces to not figure out that ADIRU 1 was giving it faulty data.
A couple of months later, QF71 encountered the same problem. Fortunately, the pilot was familiar with the QF72 incident, and simply switched the FCPC from the faulty ADIRU 1 to the backup ADIRU 2 that wasn't experiencing a problem. The flight continued without incident.
So the issue wasn't really a faulty AOA sensor, it was faulty code in both the ADIRU and FCPC, which appear to have been triggered by a rare combination of ordinary circumstances.
Note that a frozen angle of attack sensor and consequent incorrect automation responses led to the crash of XL 888, on an acceptance flight when the A320 was due to be returned to Air New Zealand after a lease.

The automation can actually be turned off, but doing so requires disabling all of the flight-control computers and dropping the aircraft into mechanical law.

Actually they disable all but one computers to drop to alternate law without any protection.

Ad XL888 there was simply no response, because the frozen sensors didn't provide the data and the problem was that the crew was testing the response at altitude where they didn't have enough to recover when the response didn't occur.

How is that possible? Isn't it the autopilot that does that? I am probably getting the wrong idea about what the autopilot does, right?

There are 2 different systems involved in this question:

The autopilot
The anti-stall system

The autopilot's role is to keep an altitude and a heading or to follow a route.
The anti-stall system's role is to prevent stalling.
In this incident, the anti-stall system was fed with incorrect data from sensors and decided that the plane needed to be pitched down to prevent stalling and did exactly that. The autopilot has nothing to do with this action.

Also, what would be the idea behind why the pilots attempt to correct the situation by pulling back the sidestick be unsuccessful at first, but suddenly have the desired effect right after he stopped giving that input?

The report states (emphasis mine):

The captain reported that he applied back pressure on his
  sidestick to arrest the pitch-down movement. He said that initially this action
  seemed to have no effect, but then the aircraft responded to his control input and he
  commenced recovery to the assigned altitude.

The pilot did not stop to give that input. The plane just did not immediately respond to it. The reason is probably that the anti-stall system was overriding his input.  According to the table on page 17, the Flight control primary computer switched from PRIM 1 to PRIM 2 on the first occurence, then from PRIM 2 to PRIM 1 on the second one, each time just before the plane started to respond to the sidestick again. This could explain the delay between input and response.

@ymb1 that would explain why the peaks where not filtered out before being fed to the computer.

@ymb1 I'd hesitate to jump to that conclusion, as no one is entirely sure why the ADIRU failed without flagging the failure, and there are other places to put blame like the bad validity and safety checks. The official report does note concerning SEE's that "The LTN-101 air data inertial reference unit (ADIRU) model had a demonstrated susceptibility to single event effects" and "the neutron fluxes for the three occurrences were at around the normal levels, [yet] this still meant there were a significant number of particles present"

I do agree with the general layout of the previous answers, I am just adding details.
Once the autopilot disconnects, the fly by wire FBW will control the flight surfaces.
If the stick is at neutral position fundamentally the FBW will maintain a « load factor » of « 1 ». Nevertheless the flight envelop will provide an alpha (AOA) protection as well a pitch protection. These protections might have cumulative protection effects
Unhappily in our case it was not a single sensor fault but an ADIRU1 fault with spikes in the following several parameters:

Spikes24 from ADIRU 1 were evident in the following parameters:
  • angle of attack
  • pressure altitude
  • computed airspeed
  • mach number
  • static air temperature
  • pitch angle
  • roll angle
  • wind speed
  • wind direction.
  The spikes appeared to be random in nature and occurred for different parameters at different times.

The ADIRU1 fault was not permanent, the very short spikes prevented the PRIMs to stop considering ADIRU1 data, because the discrepancy between every 3 similar parameters should remain at least for more than 1 second, while the spikes were very narrow, they were occurring in between the sampling period of discrepancy research.
As a consequence the spikes of the erroneous data transmitted by the faulty ADIRU concerning the AOA and the pitch angle produced the cumulative effect of the protections, however the erroneous pitching down protection durations was short and intermittent  thus allowing the pilots to correct the aircraft attitude. Once ADIRU1 has been switched off everything went ok.


text:
Are there any safety hazards when testing the F-16's fire control radar on the ground?
What are the procedures for ground testing an aircraft's fire control radar - for the F-16 or any other aircraft - and are there safety hazards associated with exposures to humans?  Most importantly, for a pregnant woman?

Your F-16 must have come with a manual!

Yes, and aircraft equipped with emitters have their arcs clearly indicated in their manuals, for example, take this diagram for the A-7E (in pink, the wider cone coming off the radome, the other areas are engine intake or turbine blade-off hazards):

There are two main ways in which a radar installation can be harmful.

Radar waves
These are the desired emission of a radar and are emitted from the antenna in a well known arc.
Based on this page by the WHO (emphasis mine):

Military radars are numerous and vary from very large installations, which have large peak (1 MW or greater) and average powers (kW), to small military fire control radars, typically found on aircraft. Large size radars often evoke concern in communities living around them. However, because its power is radiated over a large surface area, the power densities associated with these systems vary between 10 and 100 W/m2 within the site boundary. Outside the site boundary RF field levels are usually unmeasurable without using sophisticated equipment. However, small military fire control radars on aircraft can be hazardous to ground personnel. These units have relatively high average powers (kW) and small area antennas, making it possible to have power densities up to 10 kW/m2. Members of the general public would not be exposed to these emissions because during ground testing of radars access to these areas by all personnel is prohibited. The military also use most other types of radars described below.

The specific risks are listed as:

Possible health effects
  Most studies conducted to date examined health effects other than cancer. They probed into physiological and thermoregulatory responses, behavioural changes and effects such as the induction of lens opacities (cataracts) and adverse reproductive outcome following acute exposure to relatively high levels of RF fields. There are also a number of studies that report non-thermal effects, where no appreciable rise in temperature can be measured.
Cancer-related studies: Many epidemiological studies have addressed possible links between exposure to RF and excess risk of cancer. However, because of differences in the design and execution of these studies, their results are difficult to interpret. A number of national and international peer review groups have concluded that there is no clear evidence of links between RF exposure and excess risk of cancer. WHO has also concluded that there is no convincing scientific evidence that exposure to RF shortens the life span of humans, or that RF is an inducer or promoter of cancer. However, further studies are necessary.
Thermal effects: RF fields have been studied in animals, including primates. The earliest signs of an adverse health consequence, found in animals as the level of RF fields increased, include reduced endurance, aversion of the field and decreased ability to perform mental tasks. These studies also suggest adverse effects may occur in humans subjected to whole body or localized exposure to RF fields sufficient to increase tissue temperatures by greater than 1°C. Possible effects include the induction of eye cataracts, and various physiological and thermoregulatory responses as body temperature increases. These effects are well established and form the scientific basis for restricting occupational and public exposure to RF fields.
Non-thermal effects: Exposure to RF levels too low to involve heating, (i.e., very low SARs), has been reported by several groups to alter calcium ion mobility, which is responsible for transmitting information in tissue cells. However, these effects are not sufficiently established to provide a basis for restricting human exposure.

Incidental radiation
@Dohn Joe pointed out that a secondary danger of radars, which is actually common to most high frequency energy sources: incidental radiation in the form of high energy photons (X-rays) generated in parallel to the desired radiation. Basically, the process used to generate high frequency electromagnetic waves is not 100% efficient, meaning some energy goes into generating other stuff, like heat, or X-rays. Note that at these energy levels it is often more common to use particle theories instead of waves, since they are the same.
This phenomenon led to a number of health cases in Germany in the 2000s (link in German), when crews who had worked on radar systems in the '60s and '70s without adequate protection developed health complications. Some also passed them on to their children due to genetic damage.
A report dealing with the dosage rates for technicians can be found here. One conclusion that stands out is that the effects and dosage rates were heavily dependent on the position of the operator, since x-rays attenuate when travelling through any media, and while air is not the best shielding material, it does help.
To obtain a rough estimate of how far would this incidental radiation propagate, we can run some numbers. The F-16 has had a number of radars along its service life, but we will use the AN/APG-68 radar introduced in the F-16C/D Block 25 as it is the one with the most readily available information.
X-ray attenuation follows this exponential formula:
$$
I/I_0 = e^{-\mu \rho x}
$$
Where $I/I_0$ is the ratio of energy after attenuation to the original energy, $\mu$ is the linear attenuation coefficient, $\rho$ is the density of the medium and $x$ is the distance traveled. It is important to know the energy of the emitted particles as $\mu$ is different at different energies. Wikipedia gives the peak operating voltage in the Traveling Wave Tube of the AN/APG-68 as 24kV, which should limit the theoretical energy of any emitted photons to 24keV.
Taking $I/I_0 = 1/e$ we can obtain the distance after which the intensity will have been reduced to about 36.7% of the original. Taking $\mu= 0.56585\,cm^2/g$ (from here, interpolating for 25keV) and $\rho = 0.0012\, g/cm^3$, we obtain $x=1472.7\,cm$.
This means that after about 15 meters the intensity will have dropped by almost two thirds, and it will continue doing so for every 15 meters afterwards. This is a conservative value, the real distance should be less due to moisture in the air and a lower median energy in the emitted beam, meaning that even if the equipment was improperly shielded, the risks should be limited to people working directly on the radar.

In the German Armed Forces a number of personell suffered health problems due to exposure to Radar radiation from the 50s into the 80s. Unfortunately, the Wikipedia article is only available in german, and the article does not go into specifics about the situation in other countries. However, in Germany hundreds of cases were acknowledged by the Armed Forces and compensation was paid, several thousand people are still fighting for compensation. Radar can be quite unhealthy for ground crews.

@DohnJoe Those seem to be caused by X-rays produced as by-products in the amplifiers, combined with unsafe maintenance practices that exposed the crews to radiation in areas that were not supposed to be irradiated. And I can't help but note the F-104 again shows up in a negative light. Thanks, I'll add a link to the article, though I wish that page was translated into English.

According to information provided in 2002 by an anonymous informant in the Federal Ministry of Defense to the Reuters news agency, the ministry had informed all other NATO countries about the investigations in Germany. However, they had replied that they were not aware of any cancer cases in connection with radar radiation. This was partially questioned with reference to the use of identical radar equipment in all NATO states, including the USA.
Translated with www.DeepL.com/Translator

Seems like neither the original nor webarchive is loading, so I piped it through Deepl. In other words Germany informed the NATO. The others think they have had no problem. Regarding the Warsaw Pact, nothing was mentioned.

Thanks for your answers. I worked in a room adjacent to a radar test lab, that had actual F-16 Fire control radars. My son was born with a glioma, a brain cancer. Several coworkers who sat nearby have also passed away from brain cancers also gliomas. My management insists it’s coincidence and radars are non-ionizing radiation and are safe. After making my complaint my management is trying to reassign me. It seems impossible to prove my case and the information I need is not available to me, I know there are TO’s for in regards to keeping ground personnel safe when the radars are on a plane,

The radar itself is not ionizing, the electronic devices used to generate the beam might emit some ionizing radiation. Sadly that would require knowing the intricacies of the emitter, specifically of the Traveling Wave Tube, the shielding employed and the testing procedures. I've updated the answer with some more information.


text:
What types of aircraft perform military airlift operations?
What planes are the key players in military airlifting?
I know the C-130J, C-17 and A400M are among them, what others are there?
What are the key differences between the above mentioned planes?

There is no single "key player". It depends on the task. You need big, long-haul transporters like the C-5 or the An-124 to move large amounts of troop and equipment quickly. This is called strategic airlifting and is done with turbofan-powered aircraft which are similar to airliners. But they need prepared and secured air strips of considerable length (the NATO standard airstrip is 8000ft long).And then you need tactical transporters which can fly as close to the action as possible, and they must have STOL capabilities and defensive equipment to survive their missions. This requires mostly turboprop powered planes like the C-130, the C-160 or the An-12 for big equipment or the CASA 235 or the An-26 for smaller units or parts. The C-17 was meant to be a strategic airlifter with some tactical capabilities, but it cannot replace the smaller turboprops entirely. The A-400 and the An-70 are large tactical transports with some strategic capabilities, but this comes at the expense of usability on unprepared or improvised airstrips.
And then you need helicopters for the missions which require the highest amount of flexibility and closeness to the action.
All three depend on the other, and only together they become effective. That is why I cannot give you a key player.

Key characteristics of strategic transporters:

turbofan engines
swept wings, high flight Mach number and range
high wing, so the fuselage is close to the ground for easy loading and unloading
large nose doors and/or ramp in rear fuselage.

Key characteristics of tactical transporters:

turboprop engines (mostly)
straight wings with extensive high-lift devices for STOL capabilities
moderate flight Mach number and range
high wing, so the fuselage is close to the ground for easy loading and unloading, low loading of landing gear for soft ground capabilities
ramp in rear fuselage.

Key characteristics of helicopters

that whirly thing on top

"that whirly thing on top" +1

And there's the V-22, "those whirly things on the sides."

In the past, the military has contracted a great deal of their airlifting, both of personnel and freight, to commercial carriers. If you include this activity, a number of other airplanes would have to be included, and of these, the 747 would be the workhorse of the group, especially in the 1990s. In addition to regular, ongoing military contracts and charters, they also had the CRAF (Civil Reserve Aircraft Fleet) program in which they subsidized the conversion of 747 pax aircraft to freighters with the proviso that if there was a CRAF activation, those aircraft and their civilian crews would be at the disposal of the military. Indeed, when Operation Desert Shield came along, there was a CRAF activation from 17 Aug 1990 to 24 May 1991.

This is ironic, given that the 747 was the loser in the competition with Lockheed's entry, which became the C-5. The characteristic hump of the 747 still betrays this heritage - by lifting the cockpit up and out of the way, the full height of the fuselage could be accessed through the folding nose. Only the European spoilsports would argue that Boeing used that military design competition to have the government help fund it's next airliner, choosing a low wing which gave Lockheed's entry a clear headstart, right?

@PeterKämpf: It shows how the military requirements for operating without infrastructure interfere with other more desirable features of such aircraft. Because 747 is very successful freighter—the high nose door are still useful while otherwise it is designed for aerodynamic efficiency and thus lower operating cost—while no civilians ever ordered Galaxy.

I've read civilian carriers in the USA lobbied to get share of the military airlifting, so they did. After the second war, US Army had well developed airlift capacity and lot of experience from the India-China airlift and Berlin airlift, but the airline lobbyists persuaded government to downsize it and contract supplying of the overseas units instead.